1. Field of the Invention
The present invention generally relates to a compact single-stage electronic ballast circuit for emergency lighting applications, and more particularly, to a compact single-stage electronic ballast circuit, having the features of battery charging, discharging and lamp ballasting so as to reduce the fabrication cost by simplifying the circuit configuration and reducing the number of employed active switching elements.
2. Description of the Prior Art
The use of a multi-stage power converter suffers from increased volume and weight. Such a multi-stage power converter employs a considerable amount of elements, which results in high fabrication cost. Furthermore, the overall power conversion efficiency may also decrease due to multi-stage conversion. These drawbacks are unacceptable since the modern-day standards require high efficiency, low cost, small volume and lightness. Therefore, efforts have been made to provide single-stage converters with multiple functions so as to overcome the foregoing problems.
With the rapid development in power conversion technology, the safety regulations have become strict. A state-of-the-art electrical power conversion system is required to possess various functions. An UPS (uninterruptible power supply), for example, employs a charger and a discharger to assist the storage and/or the release of power and a converter to convert direct-current (DC) voltages into alternate-current (AC) voltage so as to provide required power during the electricity interruption. Furthermore, an electronic ballast or a DC power converter with the function of active power factor correction is used an additional stage of power converter to perform unit power factor.
Accordingly, a single-stage system integrating a plurality of power converters to reduce the fabrication cost has become a tendency.
To date, electronic ballasts for emergency lighting applications are exemplified as below.
Please refer to FIG. 1A, which is a commonly used circuit configuration in the prior art. When the electricity is provided normally, the switch S1 is turned on. The power passes through the half-bridge series-resonant parallel-loaded electronic ballast to light up the lamp. Also, the electricity passes through the flyback charger to charge the battery. Furthermore, the switch S2 is turned off, preventing the battery from discharging. On: the contrary, when the electricity is provided abnormally, the battery voltage VB is increased by the flyback discharger to a voltage level under normal electricity, thus lighting up the lamp by the electronic ballast.
FIG. 1B shows a modification of the circuit in FIG. 1A, in which the charger and the discharger are integrated and bi-directional switches M3 and M4 are used to implement bi-directional charging/discharging. When a charger is concerned, a flyback circuit is formed of M3 and D4 to charge the battery; and when a discharger is considered, a flyback circuit is formed of M4 and D3 to increase the battery voltage to a voltage level under normal electricity. It is obvious from the above discussion that, under proper control, the active switches M3 and M4 can be used to implement bi-directional charging/discharging.
Even though the prior arts disclosed in FIG. 1A and FIG. 1B can achieve electronic ballasts for emergency lighting applications, these circuit configurations suffer from a large number of elements and high fabrication cost. Therefore, the present invention provides an integrated single-stage converter circuit as shown in FIG. 2, in which only two active switches MS1 and MS2 are required. The single-stage converter circuit according to the present invention can, with reduced cost and volume, achieve the same functions as the prior arts disclosed in FIG. 1A and FIG. 1B. Furthermore, the active switches MS1 and MS2 have high efficiency due to a zero voltage switching (ZVS) turn-on feature.
Therefore, the present invention has been made to solve such problems in view of the forgoing status and to further provide an electronic ballast that functions as a multi-conversion to store power in the battery by a charger when electricity is provided normally and to achieve emergency lighting by a discharger when electricity is interrupted.
The present invention integrates a charger, a discharger and an electronic ballast as a single-stage circuit so as to simplify the circuit configuration and to reduce the cost. In addition, the related reports only emphasize on a lamp lighting system of high-voltage power source without high-frequency voltage conversion. In the present invention, a 12-volt battery is employed to light up the lamp. However, the DC voltage for an electronic ballast is 156V (the rectified and filtered value of the provided electricity 110Vrms) Therefore, a transformer for increasing low voltage to high voltage is required. To date, researches of a single-stage converter with such a transformer for emergency lighting applications have never been found in publications such as patent applications and journal papers.
The primary object of the present invention is to implement an electronic ballast for emergency lighting applications by using a minimize number of elements to reduce the size and cost.
Other and further features, advantages and benefits of this invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings are incorporated in and constitute a part of this application and, together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like arts throughout the disclosure.
The objects, spirits and advantages of the preferred embodiment of the present invention will be readily understood by the accompanying drawings and detailed descriptions, wherein:
FIG. 1A is a circuit configuration of a conventional electronic ballast for emergency lighting applications in the prior art;
FIG. 1B is a circuit configuration of another conventional electronic ballast for emergency lighting applications in the prior art;
FIG. 2 is a circuit configuration of a single-stage electronic ballast for emergency lighting applications in accordance with the preferred embodiment of the present invention;
FIG. 3A is a circuit configuration having the functions of a charger and an electronic ballast, showing that the switch MS1 is turned off and the current flows through the diode DS1, in accordance with the preferred embodiment of the present invention;
FIG. 3B is a circuit configuration having the functions of a charger and an electronic ballast, showing that the switch MS1 is turned off and the switch MS2 is turned on, in accordance with the preferred embodiment of the present invention;
FIG. 3C is a circuit configuration having the functions of a charger and an electronic ballast, showing that the switch MS2 is turned off and the diode DS1 is turned on, in accordance with the preferred embodiment of the present invention;
FIG. 4A is a circuit configuration having the functions of a discharger and an electronic ballast, showing that the switch MS1 is turned on, the switch MS2 is turned off and the current flows through the diode DS2, in accordance with the preferred embodiment of the present invention;
FIG. 4B is a circuit configuration having the functions of a discharger and an electronic ballast, showing that the switch MS1 is turned on and the switch MS2 is turned off, in accordance with the preferred embodiment of the present invention;
FIG. 4C is a circuit configuration having the functions of a discharger and an electronic ballast, showing that the switch MS1 is turned off and the diode DS2 is turned on, in-accordance with the preferred embodiment of the present invention; and
FIG. 5 is a circuit configuration for analyzing a series-resonant parallel-loaded in accordance with the preferred embodiment of the present invention.